1. Field of the Invention
This invention relates to a long-lasting, generally tubular, rubber or elastomer-based seal having a configuration for sealing against tubular members or drillstring components movable longitudinally through the seal, such as stripper rubber seals for rotating control heads, rotating blowout preventers, diverter/preventers and the like, used in oil, gas, coal-bed methane, water or geothermal wells.
2. Description of the Related Art
In the drilling industry, seals are used in various applications including rotating blowout preventers, swab cups, pipe and Kelly wipers, sucker rod guides, tubing protectors, stuffing box rubbers, stripper rubbers for coiled tubing applications, snubbing stripper rubbers, and stripper rubbers for rotating control heads or diverter/preventers. Stripper rubbers, for example, are utilized in rotating control heads to seal around the rough and irregular outside diameter of a drillstring of a drilling rig. Stripper rubbers are currently made so that the inside diameter of the stripper rubber is considerably smaller (usually about one inch) than the smallest outside diameter of any component of a drillstring. As the components move longitudinally through the interior of the stripper rubber, a seal is continuously effected. Stripper rubbers are self-actuating in that as pressure builds in the annulus of a well, and in the bowl of the rotating control head, the vector forces of that pressure bear against the outside surface or profile of the stripper rubbers and compress the stripper rubber against the outside surface of the drillstring, thus complementing resilient stretch fit forces already present in the stripper rubber. The result is an active mechanical seal which increases sealability as well bore pressure increases.
Stripper rubbers seal around rough and irregular surfaces such as those found a drill pipe, tool joints, and a Kelly, and are operated under well drilling conditions where strength and resistance to wear are very important attributes. In utilizing stripper rubbers in rotating control heads, the longitudinal location of the rotating control head is fixed due to the mounting of stripper rubbers onto bearing assemblies which allow the stripper rubbers to rotate with the Kelly or drillstring but restrain the stripper rubbers from longitudinal movement. Thus, relative longitudinal movement of the drillstring including the end to end coupling areas of larger diameter joints and the larger diameter of tools that bear against a stripper rubber thereby causing wear of the interior surface of the stripper rubbers.
The wear upon stripper rubbers will, over a period of time, cause a thinning of the stripper rubber to the point that the stripper rubber will fail. Such wear is enhanced or increased when multiple lengths of a drillstring are moved through the stripper rubbers, such as when a drillstring is "tripped" into or out of the well. Longer wear of stripper rubbers has been a long felt need in the industry. The advantage of a longer lasting stripper rubber is not only one of safety, but also one of expense since a longer lasting stripper rubber will reduce the number of occasions when the stripper rubbers must be replaced, an expensive and time consuming undertaking.
It is generally known that the mechanical properties of rubber-based products may be enhanced through the addition of para aramid fibrillated short fibers (pulp) and para aramid dipped chopped fibers (DCF) in applications such as hoses, V-belts and tires. Akzo Noble Fibers, Inc. of Conyers, Ga. through its European operation is one manufacturer of such reinforcing products, selling a product under the trademark Twaron.RTM.. A similar product is available from another manufacturer under the trademark Kevlar.RTM.. Twaron.RTM. is Akzo's organic manmade high performance para aramid fiber. Its chemical designation is poly (para-phenylen terephthalamid).
Twaron.RTM. fibers have been used in transmission belts where short fiber reinforced rubber is located under the cord layer, the short fibers being oriented perpendicular to the surface that transfers power. The increased hardness of the rubber in the fiber direction gives the transmission belt a lower friction coefficient, a reduced noise level when in service, a lower heat build up during cyclic compression and an increase in transmission capability. Twaron.RTM. fibers have also been used in the manufacture of hoses such as an automotive heater hose which is reinforced with a knitted (para aramid) continuous filament yarn construction. Para aramid pulp has also been used in the inner liner of grated high pressure hoses to provide an increased green strength of the liner and an improved production stability, coupling retention and better fatigue resistance.
Twaron.RTM. fibers are also utilized in tires. In the bead area, aramid short fibers give fewer mixing problems than high levels of high surface area carbon blacks. Advantages are offered by the high anisotropy and the increased dynamic modulus leading to a lower heat build-up which extends the life of the bead compound and preserves the adhesion between bead wire and bead compound. When short fibers are used in a tire tread compound, advantages include a lower rolling resistance of the tire, better water drainage, more uniform wear and possibly less noise.
In an article entitled Short Para Aramid Fiber Reinforcement published in Rubber World in June, 1994, van der Pol and de Vos of Akzo Nobel Fibers disclosed that para aramid pulp or DCF may provide certain advantages for rubber seals and oilwell packings including better mechanical properties at elevated temperatures, less creep, higher abrasion resistance and less swelling by solvents. Van der Pol and de Vos taught that short fibers provide abrasion resistance to rubber and suggested using Akzo's Twaron.RTM. fibers in applications such as V-belts, footwear, seals, rolls, tank-pads, gaskets, automotive hoses, conveyor belts, pneumatic tires, protection of mines and dams and roofing. This article is incorporated by reference.
In spite of the general knowledge pertaining to enhancing properties of rubber, there remains a long-standing problem of wear in seals and wipers used for drilling components. Wear is caused by relative movement of a drillstring or production well component against the rubber seal or wiper. Wear is present in all drilling and production applications where a rubber seal or wiper is subjected to the relative movement of a component such as drillstring tools, Kelly, pipe, or rod for the purpose of sealing, wiping, stripping, snubbing and/or packing off well fluids when drilling or producing oil or gas from a well. There remains a long-felt need for a rubber seal or wiper that is resistant to wear and capable of a longer service life than has been heretofore possible.